ARM: dts: ZII: update MDIO speed and preamble

Update MDIO configuration with ZII devices to fully utilize
MDIO endpoint capabilities.  All devices support 12.5MHz clock and
don't require MDIO preable.
Signed-off-by: Chris Healy <cphealy@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi

@@ -719,6 +719,8 @@ &fec {
 	mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		clock-frequency = <12500000>;
+		suppress-preamble;
 		status = "okay";
 
 		switch: switch@0 {

arch/arm/boot/dts/vf610-zii-cfu1.dts

@@ -158,6 +158,8 @@ fixed-link {
 	mdio1: mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		clock-frequency = <12500000>;
+		suppress-preamble;
 		status = "okay";
 
 		switch0: switch0@0 {

arch/arm/boot/dts/vf610-zii-dev.dtsi

@@ -137,6 +137,8 @@ fixed-link {
 	mdio1: mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		clock-frequency = <12500000>;
+		suppress-preamble;
 		status = "okay";
 	};
 };

arch/arm/boot/dts/vf610-zii-spb4.dts

@@ -119,6 +119,8 @@ fixed-link {
 	mdio1: mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		clock-frequency = <12500000>;
+		suppress-preamble;
 		status = "okay";
 
 		switch0: switch0@0 {

arch/arm/boot/dts/vf610-zii-ssmb-dtu.dts

@@ -105,6 +105,8 @@ fixed-link {
 	mdio1: mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		clock-frequency = <12500000>;
+		suppress-preamble;
 		status = "okay";
 
 		switch0: switch0@0 {

arch/arm/boot/dts/vf610-zii-ssmb-spu3.dts

@@ -133,6 +133,8 @@ fixed-link {
 	mdio1: mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
+		clock-frequency = <12500000>;
+		suppress-preamble;
 		status = "okay";
 
 		switch0: switch0@0 {